1. Field of the Invention
This invention relates to a photonic network packet routing method and a packet router for a photonic network that are adapted for use in a photonic network utilizing optical fibers as transmission lines for transmitting information among many locations and that, at the time of transmitting packets labeled with destination addresses, distribute the packets onto appropriate optical paths at nodes for combining multiple optical pulses.
2. Description of the Prior Art
Photonic network technologies for point-to-point transmission of information converted into optical signals have been applied to networks to create photonic networks. When, for example, the objective is to configure a network for transmitting Internet protocol (IP) packets over a photonic network, i.e., an IP-over-photonic network, photonic IP routers are required for switching the IP packets according to the IP addresses.
FIG. 13 is a conceptual diagram of conventional photonic IP routing. The diagram shows how a photonic IP router processes an IP packet group consisting of first, second and third packets (Packets #1, #2 and #3) respectively labeled with IP addresses Addresses #2, #3 and #1. When Packet #1, Packet #2 and Packet #3 are input in time series through an optical signal input (IN) of the photonic IP router in the order mentioned, the photonic IP router switches Packet #1 labeled with IP Address #2 through a second output port (OUT 2), Packet #2 labeled with IP Address through a first output port (OUT 1). In other words, the function of the photonic IP router is to read the addresses of the IP packets and switch each packet to the port appropriate for its address.
FIG. 14 schematically illustrates the configuration of a photonic IP router 140 having N number of output ports. IP packets input through an optical input port (IN) are sent along two branches to both an address processing section 141 and a switching section 142.
In the address processing section 141, a photodetector 141a converts each IP packet into an electric signal, a signal processor 141b reads its IP address and supplies the packet's routing information to a controller 141c. The controller 141c uses the routing information to produce a control signal specifying the destination (one of the 1 s′ to Nth ports) of the packet and sends the control signal to the switching section 142.
In the switching section 142, an optical delay unit 142a delays each received packet and then forwards it to a 1×N optical switch 142b for switching each input to one of the N number of output ports. When each IP packet is input to the 1×N optical switch 142b, the 1×N optical switch 142b is switched to the appropriate port by the control signal from the controller 141c of the address processing section 141. The IP packet is therefore output from the output port appropriate for the IP address of the IP packet.
Thanks to recent advances in photonic device technology, the optical switch 142b can have a switching speed faster than 1 ns (equivalent to 1 GHz). Switching speeds faster than 100 Ps have been achieved in the laboratory.
Still, increasing the switching speed of the optical switch 142b does not increase the routing speed of the photonic IP router 140 as a whole because the processes between reading the IP address of the photoelectrically converted optical signal and control of the optical switch 142b by the controller 141c are conducted electrically. Since the arrival of the control signal from the controller 141c at the optical switch 142b is therefore delayed, each IP packet sent to the switching section 142 must therefore be delayed by the same amount by the optical delay unit 142a so that it will arrive at the 1×N optical switch 142b at the same time as the corresponding control signal. The routing speed is slowed in proportion to the delay.
The main object of this invention is to provide an ultra-fast packet routing method and a packet router capable of reading IP addresses from optical signals.
The present invention, accomplished for overcoming the foregoing problem, achieves high-speed routing by enabling all processing of IP packet addresses in the processing section (processing for selecting the course along which IP packets are to proceed) to be conducted optically rather than electrically, thereby eliminating a major roadblock to routing speed enhancement.